Exploring critical conditions as a new tool for enhancing electrocaloric properties of Ba-based lead free ceramics (CritEC)
Project code: PN-III-P1-1.1-TE-2019-1689
Project number: TE1/25.08.2020
Funded by the Executive Unit for Financing High Education, Research, Development and Innovation, CNCS – UEFISCDI
New solid state refrigeration techniques are based mainly on two principles: adiabatic demagnetization cooling or adiabatic depolarization cooling. The last one is called electrocaloric refrigeration and it employs the electrocaloric effect (ECE) which consist in the change in temperature of a material upon the application or removal of an electric field, under adiabatic conditions. Ferroelectrics and relaxors are regarded as promising candidates that can easily find out their giant ECE because of their large polarization and their field and temperature-induced structural transitions, however they are usually Pb-based materials which should be replaced with environmentally friendly equivalent oxides.
Among the ferroelectric Pb-free systems, BaTiO3 family has been studied quite extensively for EC applications, but at fundamental level some problems were never elucidated like for example, if there is an optimal size and composition in BaMxTi1-xO3 systems for which the ECE can be maximized. Our idea is to explore the possibility of enhancing the ECE by using critical conditions, i.e. compositional or temperature-induced structural phase transitions, morphotropic phase boundaries or critical scale effect, if present. The aim of the present project is to develop a complex modelling-experimental approach to understand the role of composition and grain size under critical conditions in enhancing electrocaloric properties of BaTiO3-based lead-free ferroelectric ceramics. For this aim, BaMxTi1-xO3 (M4+=Sn/Zr/Ce/Hf) dense ceramics, with compositions near the tri-critical point and variable grain sizes will be comparatively investigated and their EC properties will be explored and described by appropriate models. The project will develop original models for describing size dependent properties in BaTiO3-based solid solutions with phase superposition and will develop for the first time in Romania a methodology for measuring and evaluating the ECE in ferroelectric ceramics.